Functions may be added or overlaid onto preexisting objects by extending associated code lists. Code lists can enumerate design time entities, such as process component code, object type code, and service interface code. Likewise, code lists can label configuration entities. Codes may be used for business object persistence, messages, and for foreign key relationships in system and configuration tables.
Some codes are based on official standard code lists, like ISO codes or United Nations Centre for Trade Facilitation and Electronic Business (UNCEFACT) codes, many of them are developed by backend providers, independent software vendors, or customers.